Smartcard Reminder

Overview

I frequently forget to remove my SmartCard from my computer before leaving the office.
It would be incredibly convenient to have some kind of audible reminder for this.
When I was issued the smart card I agreed that I would not interface with it as a company policy.
While it is likely possible to only access the reader to determine if a smart card is present without accessing the smartcard itself, I'd rather not risk gaining the ire of the local security. Also there is a company policy that unofficial software should not be installed on company machines.

The idea is relatively simple, use a microntroller to read the status of a line-of-sight (LOS) sensor, such as an IR beam. Mounting the sensors to the computer, it can be determined if the card is present, and blocking the IR beam. A second set of LOS sensors would be mounted to the office exit, also monitored by the microcontroller.

When the door LOS sensor is tripped, the microntroller will check the status of the card LOS sensor. If the card is interrupting the beam, then card is present, and a piezo buzzer will be activated to inform the user that it has left the area without its security card.
User hits a button to reset the alarm, grabs his card and exits.

To compensate for the system not knowing the difference between the card holder and a visitor breaking the doorway beam, a second set of LOS sensors will need to be mounted to either side of the room entrance. Depending on which set of beams is broken first, the alarm will or will not activate.
The alarm will then be set to allow one beam breakage in the opposing direction as the guest leaves. Unsure about how to compensate for guests standing in the doorway, as they often do.